This invention relates to a method for manufacturing a semiconductor device such as a transistor having an n-type region in a p-type region.
In semiconductor devices like transistors, an emitter region is formed by diffusing arsenic with a low diffusion speed in order to form a shallow emitter-base junction. However, vapor diffusion of arsenic, which is poisonous, involves a risk. On the other hand, solid arsenic diffusion by using arsenic-doped silicate glass (AsSG) will frequently cause lattice defects at the interface between such glass and substrate, leading to deterioration in electrical characteristics. Moreover, transistors which have an emitter region formed by the use of arsenic are subject to very low emitter-base reverse withstand voltage.
In order to eliminate the above defects of the arsenic diffusion, there has been proposed the use of phosphorus as an impurity. Having a substantially higher diffusion coefficient when compared with arsenic, however, phosphorus requires a low-temperature diffusion process. In addition, such low-temperature diffusion may not allow satisfactory getter treatment of alkali metals such as sodium that may exist at the interface between an insulating film and semiconductor substrate. Furthermore, in implanting phosphorus ions into the semiconductor substrate by the ion-implantation method, these phosphorus ions must be activated at a temperature of approximately 950.degree. C. to 1,000.degree. C. after such implantation. Such high-temperature treatment will, however, rediffuse the impurity to prevent high-accuracy control of diffusion depth.